This invention relates to a method of automatically controlling a dust-collecting plant, in which a plurality of gas streams are sucked from spaced apart dust sources and in a manifold are supplied to a dust-collecting unit and the gas is exhusted into an exhaust gas chimney by an automatically controlled exhaust fan.
Such plants are usually operated in such a manner that a constant pressure in the manifold is maintained by automatic control and the negative pressures at each dust source must be manually adjusted only once, or that one dust source is automatically controlled for a control of the entire system. Both modes of operation will not produce reasonably satisfactory results if there are substantial fluctuations at any point of the dust-collecting plant. In such cases the known methods of automatic control will be inadequate because they must be performed with a large margin of safety in order to ensure an optimum dust collection. This means that excessively high negative pressures are adjusted and gas is sucked at excessively high rates. In such plants the exhaust fan is oversized, as a rule, and is operated during most of the time at less than its optimum efficiency and still has an excessively high power requirement. For this reason the capital investment and the operating costs are unreasonably high so that the expenditure involved in dust collection is unnecessarily increased.
An example of a dust-collecting plant comprising a plurality of spaced apart sources from which gas is sucked is found in steelmaking plants, which include a main dust-collecting plant associated with the converter and increasingly comprise dust-collecting plants for treating and purifying gas from the so-called secondary dust sources. Some dust sources found in steelmaking plants and the rates at which gases become available in such sources under different operating conditions are compiled in the following Table.
______________________________________ Rate Dust Source Mode of Operation m.sup.3 /h ______________________________________ Reladling pit Continuous sucking 25,000 Reladling 205,000 Slagging stand Slagging 105,000 Hot mixer Continuous sucking 12,500 Charging 200,000 Removing 200,000 Converter Charging scrap 1,235,000 Charging hot metal 1,875,000 Making crude steel 575,000 Discharging crude steel 820,000 and slag Argon scavenging Scavenging 260,000 plant ______________________________________